System and method for determining air interface information for radio resource management in wireless communications

ABSTRACT

A method for determining values for use by radio resource management functions is disclosed. Air interface actual values and predictive values are obtained and stored. A timestamp indicating a time when each actual value or predictive value is obtained is generated and stored. The actual values and the predictive values are processed to provide an output value.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/318,402, filed Dec. 23, 2005, which is a continuation of U.S. patentapplication Ser. No. 10/748,015, filed Dec. 30, 2003, now U.S. Pat. No.7,050,412, issued May 23, 2006, which claims priority from U.S.Provisional Patent Application No. 60/480,844, filed Jun. 23, 2003,which are incorporated by reference as if fully set forth herein.

FIELD OF INVENTION

The present invention relates generally to wireless communicationsystems. More particularly, the invention is useful for wirelesscommunication systems which use air interface values for radio resourcemanagement.

BACKGROUND

The purpose of radio resource management (RRM) in wireless communicationsystems is to efficiently manage the use of resources over the airinterface (i.e., radio resources). Intelligent management of radioresources is essential for maximizing the air interface capacity,ensuring connection reliability and network stability and reducing thebattery consumption of wireless transmit/receive units (WTRUs).

Typical RRM functions include: (1) call admission control, which acceptsor rejects requests for new radio links based on the system load andquality targets; (2) handover control, which ensures that a call(connection) is not dropped when a WTRU moves from the coverage area ofone cell to the coverage area of another cell; (3) power control, whichmaintains interference levels at a minimum while providing acceptablelink quality; (4) radio link maintenance, which ensures that quality ofservice requirements for individual radio links are satisfied; and (5)congestion control, which maintains network stability in periods of highcongestion.

RRM functions are triggered, and make decisions, based upon a variety ofinputs. Among these inputs, air interface measurements observed by theWTRU and the Node B are extensively used. Air interface measurements canoriginate from either the WTRU or the Node B. WTRU measurements andradio link specific Node B measurements are referred to as dedicatedmeasurements. Cell-specific Node B measurements are referred to ascommon measurements. Both types of measurements are employed toprecisely evaluate the current state of the radio environment. Forexample, interference measurements can be used to decide the allocationof physical resources in a timeslot or frequency band.

Typical measurements which RRM functions rely upon for evaluating thestatus of the radio environment include: interference signal code power(ISCP); received power measurements (both individual radio link andreceived total wideband power (RTWP)); received signal strengthindicator (RSSI); transmission power, (including individual radio linkpower and total power); and signal-to-interference ratio (SIR)measurements. These measurements are just several examples of the manymeasurements that are applicable with the proposed invention.

As will be described hereinafter, some of these measurements may bepredicted and a combination of their latest reports and theirpredictions may be used when the system is in a transient phase.

Unfortunately, there is a drawback in the manner in which current RRMfunctions are performed. There are several conditions that may cause theaforementioned measurements to be unavailable or invalid. First, it ispossible that measurements are simply not reported, or measurementreports are corrupted over the air interface. For example, WTRUmeasurement reports are eventually encapsulated into transport blocks(TBs) to which cyclic redundancy check (CRC) bits are attached. The NodeB physical layer determines whether an error occurred by examining theCRC bits. In the event of an error, the Node B physical layer may eitherdeliver the erroneous TB to upper layers with an error indication, orsimply indicate to upper layers that an erroneous TB was received on aparticular transport channel or a set of transport channels. Such ascenario is particularly relevant when considering WTRU measurementssince they are sent over the air interface.

Secondly, measurements generally have an age threshold, after which themeasurement is considered invalid. If measurement reports are notfrequent enough, it is possible that valid measurements will eventuallybecome invalid, and thus unavailable to RRM functions.

Finally, it is possible that measurements are simply invalid because theradio link or the system has entered a transient phase that isundergoing stabilization. For example, interference measurements areunstable for a certain period of time (up to ½ second) following theconfiguration or reconfiguration of a radio link due to the transientphase of the power control. Such measurements should not be used totrigger RRM functions or to make decisions since the current state ofthe radio link or the system is unstable.

Accordingly, an improved system and method for obtaining measurementsfor more effective radio resource management is needed.

SUMMARY

The present invention is a radio resource control system and methodwhich manage air interface resources. According to the presentinvention, a wireless communication system obtains RRM data bydetermining availability and validity of certain system measurements.First it is determined whether actual system measurements and predictedmeasurements are available, and it is also determined whether the actualsystem measurements are valid. Depending upon the results of thedetermination, a selective combination of actual air interfacemeasurements, predicted values and default values are used.Alternatively, the radio resources for which the RRM measurement isdesired may not be allocated for use.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding of the invention may be had from thefollowing description of preferred embodiments, given by way of exampleand to be understood in conjunction with the accompanying drawingwherein:

FIG. 1 is a flow diagram showing the use of different types of valuesfor RRM functions in accordance with the present invention;

FIGS. 2A and 2B are time varying weighting functions used in accordancewith the present invention; and

FIG. 3 is a centralized measurement control unit made in accordance withthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments are described herein in conjunction with anapplication of the invention for voice or data utilizing regular andHSDPA transmissions according to the Third Generation PartnershipProject (3GPP) wideband code division multiple access (W-CDMA)communication system, which is an implementation of a Universal MobileTelecommunications System (UMTS). Although 3GPP terminology is employedthroughout this application, the 3GPP system is used only as an exampleand the invention may be applied to other wireless communicationssystems where measurement-based RRM is feasible.

As used throughout the current specification, the terminology “wirelesstransmit/receive unit” (WTRU) includes, but is not limited to, a userequipment, mobile station, fixed or mobile subscriber unit, pager, orany other type of device capable of operating in a wireless environment.These exemplary types of wireless environments include, but are notlimited to, wireless local area networks and public land mobilenetworks. The terminology “Node B” includes, but is not limited to, abase station, site controller, access point or any other type ofinterfacing device in a wireless environment.

FIG. 1 is a flow diagram of a procedure 20 for determining measurementvalues for use by RRM functions in accordance with the presentinvention. First, actual measurements and predictive values are receivedand stored in a database along with a timestamp of when they werereceived (step 22). These measurements and values are received fromdifferent RRM functions such as call admission control, handovercontrol, power control and radio link maintenance. Regardless of whetherthey are actual system measurements or predictive values (such as, forexample, in the case of the call admission control function whichpredicts the system impact upon acceptance of a new call), they arestored in a database. The RNC maintains the database of both themeasurements and values and when they were stored.

Each time the RNC receives a measurement or value, it stores it in thedatabase along with a timestamp corresponding to the time at which it isreceived. By doing so, the RNC can subsequently determine ifmeasurements or values are available (i.e., stored in the database) andif so, if they are valid with respect to their age (i.e., their age isless than a certain age threshold).

If an RRM measurement request has not been received as determined atstep 30, no further action is taken other than to continue to receiveand store actual measurements and predictive values at step 22. If arequest for an RRM measurement has been received as determined at step30, the RNC reviews the database for the requested RRM measurement todetermine whether the requested RRM measurement is available.Measurements may be unavailable (i.e., they are not stored in thedatabase) either because no measurement report was sent or themeasurement report was corrupted over the air interface. If actualsystem measurements are not available as determined at step 34, adetermination is made as to whether predictive values are available(step 36).

The predictive values (M_(PREDICTED)) are determined as follows. Whencertain RRM functions perform an action, they can predict what certainsystem measurements, (such as interference or power), will be once theaction is performed. For example, one RRM function is the Call AdmissionControl (CAC) algorithm. The CAC algorithm predicts what theinterference and power will become once a call is added. If thepredicted levels are acceptable, then the call is added; if thepredicted levels are unacceptable, then the call is denied. Inaccordance with the present invention, these predicted interference andpower values (along with other types of predicted values) are thenstored and used as predicted values for interference and power. Sincethe prediction of RRM values is well known in the prior art for manydifferent types of RRM functions, and the particular prediction methodis not central to the present invention, it will not be described indetail hereinafter.

If predictive values are available, the predictive values are used (step38), and if not, a default value is used (step 40).

A default value is a predetermined value which is established byhistorical conditions and or a series of measurements or evaluations. Inessence, a default value is a predetermined value which is pre-storedand retrieved when desired. The default value is typically chosen suchthat RRM functions behave in a conservative way.

If actual system measurements are available as determined at step 34,then it is determined whether the actual system measurements are valid(step 42). As aforementioned, with respect to the validity of actualsystem measurements, these measurements may be invalid because they aretoo old, or may be invalid because the system is in a transient phaseand hence, the measurements do not accurately represent the state of thesystem.

With respect to the age of a measurement, when a measurement report isreceived in the RNC database, it is assigned a timestamp. The timestampcorresponds to the time at which the measurement report was received.When the measurement is retrieved from memory, its timestamp is read. Ifthe timestamp indicates that the measurement is older than a certainmeasurement age threshold (e.g., one second), then the measurement isdeemed invalid.

With respect to the invalidity of a measurement because it is taken whenthe system is in a transient period, as aforementioned, each RRMfunction is associated with one or more RRM measurements. Each time anRRM function performs an action on the system, it determines the time atwhich the action was taken. This time corresponds to the start of the“transient period.” The transition period lasts for a certain duration,after which point the system is considered stable again. The duration ofthe transient period depends on the type of action that was performed bythe RRM function. The duration of the transient period is a designparameter.

If a particular RRM measurement is taken during the transient period ofthe RRM function, it is deemed to be invalid. This can be determined inseveral ways. In a first alternative, associated with each RRMmeasurement stored in the database is an indication of whether or notthe RRM measurement was taken during the transient period. Althoughthese measurements are stored, they will be deemed invalid.

In a second alternative, a timestamp for the beginning of each RRMtransient is stored separately. When an RRM measurement is retrievedfrom the database, its timestamp may be compared to the timestamp of thetransient period. If the timestamp of the retrieved RRM measurement iswithin the transient period (i.e., the timestamp of the beginning of theRRM transient plus the duration of the transient), the retrieved RRMmeasurement is determined to be invalid.

In a third alternative, actual measurements may be declared invalid bysimply determining if a predicted measurement is in the database and ifso, determining its timestamp. This alternative assumes that thetransient period begins exactly when predicted measurements are writtento the database. These alternatives are intended to be illustrative, notlimiting, as there are many different ways that such a determination ofinvalidity may be effected.

The system determines the validity of an actual measurement in view ofboth age of the actual measurement and the stability of the system. Ifthe actual measurement is valid as determined at step 42, then theactual measurement is used (step 44).

If the actual measurement is deemed not valid at step 42, adetermination is made as to whether a predictive value is available(step 46). If a predictive value is available as determined at step 46,the actual measurement is combined with the predictive value (step 48).

The combination of actual measurements and predictive values asperformed at step 48 will now be described. Although those of skill inthe art realize that they are many different ways to combine the values,in one preferred embodiment, the present invention uses a combination ofactual measurements (M_(ACTUAL)) and predicted values (M_(PREDICTED)) asfollows:M(t)=α(t)·M _(PREDICTED)+(1−α(t))·M _(ACTUAL);  Equation (1)where α(t) is a time-varying weighting function and t represent theamount for time elapsed since the initiation of the transient period(i.e., transient period starts at t=0). M(t) represents the combinedmeasurement at time t which is provided to the RRM function. Typically,α is a monotonically decreasing function between one (1) and zero (0).Preferably α should equal 1 at t=0, immediately following the beginningof the transient period and α should equal 0 at the end of the transientperiod, once actual measurements are considered stable.

Example α weighting functions are shown in FIGS. 2A and 2B for atransient phase of 1 second duration. In FIG. 2A, the variation overtime is a substantially straight line function, whereas in FIG. 2B thevariation over time results in α initially diminishing at a slow rate,followed by a rapidly diminishing rate. This may be approximated by anexponential or geometric change, depending on the nature of α.

It is possible that succeeding actions take place during the transientperiod (i.e., before α has reached zero). When a subsequent action istaken by an RRM function, the system enters a “new” transient period.Since certain RRM functions typically predict what αvalue would befollowing an action that is taken at time t₁, the predicted value isbased on M (t₁). In this case, M_(PREDICTED) is made based on M (t₁),where t₁ is the time when the succeeding action is triggered.

Furthermore, t is reset to zero at the completion of the succeedingaction (i.e., a new transient period is started). If a new transientperiod is started, any subsequent RRM function that acts at t₂ would uset₁ as the beginning of the transient phase. As a result, t in Equation 1would be t=t₂−t₁.

Referring back to FIG. 1, if it has been determined that the actualmeasurement is not valid as determined at step 42 and predictive valuesare not available as determined at step 46, then the RNC may implementone of the following four options (step 50): (1) use a default value asin step 40; (2) combine the actual measurement with a default value; (3)add a margin to the actual measurement; or (4) declare the resources atissue to be unavailable.

With respect to the first option, use of the default value, this wasexplained with reference to step 40.

With respect to the second option, combining the actual measurement anda default value, the RNC combines these in different ways depending uponthe reason why the measurement is invalid. If the measurement is invalidbecause the latest actual measurement in the database is too old, thenan equation similar to Equation 1 can be used:M(t)=α(t)·M _(ACTUAL)+(1−α(t))·M _(DEFAULT)  Equation (2)

In Equation 2, the time-decaying α term is applied to M_(ACTUAL) and tis the elapsed time since the measurement was stored in the database.Preferably this α function differs from the one used in Equation 1 inthat it is chosen to decay much more slowly.

If the actual measurement is declared invalid because the system is in atransient state, but fresh actual measurements are available, a weightedcombination of the actual measurement and the default value is used:M=A·M _(ACTUAL) +B·M _(DEFAULT);  Equation (3)where A+B=1 and the weighting factors A and B are configurableparameters that are optimized based on simulations or observations ofthe system. Note that different measurements could have differentweighting factors.

With respect to the third option of adding a margin to the actualmeasurement, preferably a time-varying error margin is added to theactual measurement, as described by:M=M _(ACTUAL)±MARGIN;  Equation (4)where MARGIN is a time-varying margin which is large at time zero,immediately following the initiation of the transient period, andmonotonically decreases toward zero as the transient period ends. As isthe case with Equation (1), Equation (4) is executed when the actualmeasurements are available, but are deemed not to be valid due to atransient period or an expired timestamp. Note that this option is onlyvalid in the case where measurements or metrics monotonically increaseor decrease towards the converged value. In the case where measurementsor metrics oscillate around the converged value, this option is notoptimum.

This option has the advantage that predictive measurements need not bepresumed to exist during the transient period. It is further possible toexecute Equation (1) when predictive measurements are available andexecute Equation (4) when MARGIN is considered the best “prediction.”

With respect to the last option of step 50 regarding declaring resourcesto be unavailable, if it has been determined that actual measurements,predictive values, adding a margin to an actual measurement or acombination of any of these options is undesirable, the system maysimply decline to send an RRM measurement and those resources for whichthe RRM measurement was requested will be deemed by the assistant to beunavailable. Accordingly, those resources will not be used.

The result of the determination as to whether to use the actual value atstep 44, a predictive value at step 38, a default value at step 40, acombined actual measurement with a predictive value at step 48, or oneof the options in step 50, is then used to provide the requested RRMmeasurement.

To facilitate the management of measurements, a centralized measurementcontrol unit is utilized at the RNC. The centralized measurement controlunit implements the following functions: (1) storing receivedmeasurements within a central structure; and (2) measurement processing,including measurement filtering, tracking measurement age, and validity(e.g., assigning timestamp upon reception, and age threshold comparison)and selecting between or combining predicted values and actualmeasurements.

A centralized measurement control unit 80 made in accordance with thepresent invention is shown in FIG. 3. The measurement control unit 80includes a measurement setup unit 81, a measurement reception andstoring unit 82, a measurement processing unit 83 and a measurementoutput unit 84.

The measurement setup unit 81 implements the measurement setupprocedures with respect to the WTRU and the Node B. It is responsiblefor the setup and configuration of measurements. More specifically, itcommunicates with the Node B and the WTRU RRC layers to setup, modify,and end measurements, giving all measurement configuration details(e.g., averaging period, reporting criterion/period).

The measurement reception and storing unit 82 stores the actual andpredicted WTRU and Node B measurements in an organized structure. Thisincludes assigning timestamp information upon reception of a measurementin order to track the age of the measurement.

The measurement processing unit 83 filters received measurements,verifies measurement validity and/or availability and combining actualmeasurements, predicted values and default as appropriate. Themeasurement processing unit 83 is responsible for all of the measurementprocessing that is described in the present invention.

The measurement output unit 84 provides proper measurements to RRMfunctions upon request (i.e., providing actual measurements when valid,predicted measurements when unavailable or invalid or a combination ofactual measurements, predicted values and default values, such as areillustrated in FIG. 1 at steps 38, 40, 44, 48, and 50). Moreover, thismeasurement output unit 84 can optionally be responsible for triggeringRRM functions when measurements exceed a predetermined threshold.

What is claimed is:
 1. A method for determining values for use by radioresource management functions, comprising: obtaining air interfaceactual values and predictive values; storing the actual values and thepredictive values; generating and storing a timestamp indicating a timewhen each actual value or predictive value is obtained; and processingthe actual values and the predictive values to provide an output value,wherein the output value includes any one of: an actual value, apredictive value, a combination of the actual value and the predictivevalue, a default value, or the actual value plus a margin, wherein theprocessing includes: determining an occurrence of a transient period,wherein the transient period is a period of time when a radio link isunstable; and determining whether the actual value is valid by comparingthe timestamp of the actual value to the occurrence of the transientperiod, and on a condition that the timestamp is within the transientperiod, then the actual value is determined to be not valid.
 2. Themethod according to claim 1, wherein the processing includes determiningwhether the actual value or the predictive value is valid by comparingthe corresponding timestamp with a threshold, and on a condition thatthe timestamp is older than the threshold, then the actual value or thepredictive value is determined to be not valid.
 3. The method accordingto claim 1, wherein: the actual value is stored with a correspondingindicator, which indicates whether the actual value was obtained duringthe transient period; and the determining includes evaluating theindicator to determine whether the actual value is valid.
 4. The methodaccording to claim 1, wherein the processing further includes: using theactual value to provide the output value on a condition that the actualvalue is available and valid.
 5. The method according to claim 1,wherein the processing further includes: combining the actual value andthe predictive value to provide the output value on a condition that theactual value is available but not valid and the predictive value isavailable.
 6. The method according to claim 1, wherein the processingfurther includes: providing the output value using any one of: thedefault value, the combination of the actual value and the defaultvalue, the actual value plus the margin, or declaring air interfaceresources to be unavailable on a condition that the actual value isavailable but not valid and the predictive value is not available. 7.The method according to claim 1, wherein the processing furtherincludes: using the predictive value to provide the output value on acondition that the actual value is not available and the predictivevalue is available.
 8. The method according to claim 1, wherein theprocessing further includes: using the default value to provide theoutput value on a condition that the actual value is not available andthe predictive value is not available.